Wiring question for a weird phone project....

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I didn't know where to ask this question but this seemed like the right place, I apologize if its not. I'm restoring an old 1922 telephone (technically its an apartment intercom, but I'm turning it into a phone with circuitry I removed from a modern chorded phone as most of the original insides are missing anyway). The only issue I'm having is connecting the bells to a spot where they would ring upon an incoming call. I attatched the bells to a 9 volt and they worked. Is there a place on a standard phone line or on telephone circuitry where something is only powered during an incoming call but isn't powered when the reciever is picked up? I attatched some pictures of the modern phone whose insides I'm using. Thanks for any help, I know I may not have posted this in the right place. Thanks!

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You can also just build the ring filter network out of the WE 425A/B network on perfboard, if you already have everything else together. IIRC there are BSPs (Bell System Practices, lengthy paper tech docs) that include schematics of the WE 425A/B networks. Donor phones are easy to find, if you just want to grab the whole WE network tho.

Let's see pics of this apartment intercom! I've got a pair of unknown early brass intercoms I plan on converting.

EDIT: Also, if your intercom is like mine and/or rang fine on DC, it may be a set of DC bells with a mechanical interruptor, so it may not work with the AC ring signal from a POTS line. Post pics of the ringer and we can determine what kind it is.

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Here are some pics of the intercom, the bell mechanism and an old ad for the intercom which is the only information I could find on it. The intercom is mostly in pieces at the moment, so I only have one "before" picture that I took before I started working on it.

The intercom

This is the bell mechanism with the bells detatched

The top right is the one I'm working on

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Awesome find! It does look like the bells are set up for DC, though -- the spring arm mechanism toward the bottom of the picture of the bell assembly is a mechanical interruptor. What happens is, when DC is applied, the interruptor is closed, current flows into the coils of the bell, and pulls the arm in, striking one bell and ringing it. As soon as it is pulled in far enough toward the coils, the contact points on the interruptor open, current stops flowing, and the spring on the arm pulls the clapper back toward the other bell. The arm strikes the other bell and the contact points close, and the cycle repeats. Without the mechanical interruptor, applying DC would cause the arm to strike one bell and then stay in the "against the coils" position until the current was turned off.

AC bells work by using the frequency of the AC to make the arm change directions. For most ringing circuits, this is between 20 - 30 Hz. This also makes it easy to build a ring detector (it's just a DC blocing low-pass filter). Your DC bells may "just work" with AC, or they may buzz, failing to really strike the bells with enough force to ring. It looks like you can probably take the other coil wire loose and take the mechanical interruptor out of the circuit if you need to.

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Thanks that will probably come in handy. I'll definitely need to go get some materials. I have most of the restoration done now, I expect to be finished in two days...hopefully. I'm on a bit of a time constraint as a lot is going on right now. Thanks for your help, I'm probably going to rush it and use what I have laying around right now to at least have something semi-functioning and go back to work out the bells and some other issues when I get the chance. I'll post some pics in a few days when and if I'm finished. Thanks!